Regarded as a load in this context is in particular an electric motor (e.g. an asynchronous motor). A thermal overload on the load is produced by an excessive current flow. An excessive current flow may be caused, for example, by mechanical overloading of an electric motor or by a failure of one or two current circuits (phases) of the electric motor. This results in undesirable temperature changes at the load, which may ultimately lead to load damage.
To determine imminent thermal overloading of an electrical load, devices are generally incorporated in the phase via which the load is supplied with electrical energy, so that these devices can be used to detect the presence of a thermal overload. Single-phase or even multiphase monitoring can take place, i.e. a single current circuit (one phase) but also a plurality of current circuits (several phases) of the load can be monitored.
For each phase to be monitored, the corresponding devices have a current path along which the energy supplied via the phase is fed. The load's electrical energy therefore passes through the device by way of the current path. The current now of the current path is monitored by way of a monitoring unit of the device so that imminent overloading of the electrical load can be detected. Such devices are, for example, overload relays or circuit breakers. For a downstream load, a circuit breaker provides not only thermal overload protection by way of an A-release, but also short-circuit protection by way of an N-release.